1. Field of the Invention
The present invention relates to a magnetoresistive tunnel junction element for reading a magnetic field intensity from a magnetic recording medium or the like as a signal and, in particular, to a magnetoresistive tunnel junction element which has inventive biasing means and which is superior in stability of a detecting operation with respect to an external magnetic field signal.
2. Description of the Prior Art
An MR sensor based on an anisotropic magneto-resistance (AMR) or spin-valve (SV) effect is well known as a reading transducer of magnetic recording. The MR sensor can detect a change of a signal recorded in a recording medium by a resistance change of a reading portion formed of a magnetic material. An AMR sensor has a low resistance change ratio xcex94R/R of the order of 1 to 3%, whereas an SV sensor has a high resistance change ratio xcex94R/R of the order of 2 to 7%. An SV magnetic reading head indicating such high sensitivity is replacing an AMR reading head to enable reading of a very high recording density, for example, of several gigabits per square inch (Gbits/in2).
In recent years, a new MR sensor has attracted attention for its application potential in ultra-high density recording. That is, it has been reported that magnetoresistive tunnel junctions (referred to as MRTJ, or synonymously TMR) indicate the resistance change ratio xcex94R/R of12% or more. Although a TMR sensor is expected to replace the SV sensor as a next-generation sensor, an application to a magnetic head has just started, and one of outstanding problems is to develop an inventive head structure which can maximize TMR properties. That is, the TMR sensor itself has a so-called current perpendicular to the plane (CPP) geometry in which a current is passed in a thickness direction of a laminated film. Therefore, there has been a demand for a design of a new head structure which has not heretofore been proposed.
An example of application of a TMR element to a magnetic head structure is described, for example, in Japanese Patent Application Laid-Open No. 282616/1997. An element structure disclosed in the publication includes: a first magnetic layer (so-called free layer) formed of a soft magnetic material; a second magnetic layer (so-called pinned layer) having a magnetization direction crossing at right angles to a magnetization direction in an initial state of the first magnetic layer; an antiferromagnetic layer formed on the second magnetic layer; and an insulating layer, disposed between the first magnetic layer and the second magnetic layer, for tunnel-joining the magnetic layers to each other. Furthermore, respective bias magnetic layers formed of ferromagnetic materials such as CoCrPt are disposed on opposite ends of the first magnetic layer. The magnetization direction in the initial state of the first magnetic layer is regulated in a direction from one bias magnetic layer to the other bias magnetic layer by a magnetic field from the bias magnetic layer.
A rising portion of an MR curve is defined by magnetization rotation of the first magnetic layer (free layer). In order to obtain a steeper rising of the MR curve, it is preferable to completely change the magnetization direction of the first magnetic layer (free layer) with respect to a magnetic field signal by magnetization rotation. However, in actual a magnetic domain is generated in the first magnetic layer (free layer), and movement of a magnetic wall and rotation of magnetization simultaneously occur with respect to the magnetic field signal. As a result, Barkhausen noise is generated, and a problem occurs that MR head property is not stabilized. To solve the problem, the bias magnetic layers are disposed on the opposite ends of the first magnetic layer.
However, TMR has a special structure in which layers for generating a bias magnetic field (bias magnetic layers) are brought into contact only with the first magnetic layer. Therefore, it cannot be said that hard magnets have a sufficient effect in the aforementioned conventional arrangement structure of the bias magnetic layers, and instability of a magnetization rotating operation of the first magnetic layer (free layer) with respect to the magnetic field signal still remains unsolved. As a result, yield of a product in manufacturing of TMR element is remarkably bad, and this is a large problem in the manufacturing of TMR element.
The present invention has been developed under these circumstances, and an object thereof is to provide a magnetoresistive tunnel junction element which has an inventive bias magnetic field applying structure superior in stability of a magnetization rotating operation of a free layer with respect to a magnetic field signal.
To achieve the object, according to the present invention, there is provided a magnetoresistive tunnel junction element having a tunnel multilayered film in which a tunnel barrier layer, and a ferromagnetic-free layer and ferromagnetic pinned layer formed to sandwich the tunnel barrier layer therebetween are laminated, wherein a pinning layer for pinning magnetization of the ferromagnetic pinned layer is laminated on the surface of the ferromagnetic pinned layer opposite to the surface thereof contacting the tunnel barrier layer, a bias magnetic field applying layer is formed on the surface of the ferromagnetic free layer opposite to the surface thereof contacting the tunnel barrier layer, the bias magnetic field applying layer is a laminate of a nonmagnetic noble metal layer and an antiferromagnetic layer, and the ferromagnetic free layer is magnetically exchange-coupled to the antiferromagnetic layer via the nonmagnetic noble metal layer so that a bias magnetic field can be applied to the ferromagnetic free layer.
Moreover, according to a preferred embodiment of the present invention, the nonmagnetic noble metal layer is constituted of Cu, Ag, Au, Ir, Ru, Rh or Cr.
Furthermore, according to another preferred embodiment of the present invention, a thickness of the nonmagnetic noble metal layer is set to a range of 0.5 to 6.0 nm, so that a strength of the magnetic exchange coupling between the antiferromagnetic free layer and the antiferromagnetic layer can arbitrarily be set.
Additionally, according to another preferred embodiment of the present invention, the bias magnetic field applying layer is constituted to contact the whole one surface of the ferromagnetic free layer.
Moreover, according to another preferred embodiment of the present invention, a pair of bias applying means are formed to contact opposite ends of the ferromagnetic free layer in a direction in which the bias magnetic field is applied, and the bias applying means is constituted to further apply the bias magnetic field to the ferromagnetic free layer.
Furthermore, according to another preferred embodiment of the present invention, extended portions extended beyond positions of opposite ends of the ferromagnetic pinned layer in a longitudinal direction (bias magnetic field applying direction) are formed on opposite ends of the ferromagnetic free layer, the bias applying means is formed to partially contact the extended portion of the ferromagnetic free layer, and the bias applying means is constituted to apply the bias magnetic field to the ferromagnetic free layer.
Additionally, according to another preferred embodiment of the present invention, the bias applying means includes a hard magnet layer or an antiferromagnetic layer.
Moreover, according to another preferred embodiment of the present invention, the ferromagnetic free layer is constituted of a synthetic ferrimagnet.
Furthermore, according to another preferred embodiment of the present invention, the tunnel multilayered film is electrically connected to a pair of electrodes disposed opposite to each other via the tunnel multilayered film.
Additionally, according to another preferred embodiment of the present invention, the nonmagnetic noble metal layer is constituted to promote the magnetic exchange coupling between the ferromagnetic free layer and the antiferromagnetic layer.